Pre-Weakening Of Fabric Covered Airbag Doors

ABSTRACT

A variety of embodiments are disclosed, in both apparatus and method form, that relate to the use of fabric material in the manufacture of an air bag deployment system. In addition, fabric weakening is disclosed according to a technique that does not result in physical alteration of the fabric. This invention therefore includes an air bag cover for an air bag safety system for a vehicle comprising a fabric outer layer having a frontside and a backside and a substrate containing an opening wherein the opening has a periphery. The substrate is preferably formed by low pressure molding, wherein the fabric outer layer overlies the opening in the substrate, and wherein the fabric outer layer is weakened at a location that is adjacent or overlies the substrate opening periphery.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/373,332, filed Feb. 24, 2003 and published Aug. 26, 2004 as UnitedStates Patent Application Publication No. US 2004/0164531, the teachingsof which are incorporated herein by reference.

FIELD OF INVENTION

This invention relates to air bag doors used in motor vehicles toconceal inflatable restraint systems and, more particularly, to air bagdoors having fabric or textile as the top or outer surface which may bepre-weakened to allow deployment of the air bag.

BACKGROUND OF THE INVENTION

Air bag systems, or supplemental inflatable restraint systems, arecommonplace in nearly all of the motor vehicles of today to protectoccupants from serious injury upon collision or roll-over of theirvehicles. With the present consumer interest quite high for additionalfeatures in new vehicles, air bag systems have proliferated inside thecar such that they may deploy in nearly any direction and from nearlyany surface. While air bag systems were originally integrated into thehub of the steering column for forward impact protection of the driverand into the instrument panel for similar protection for the front seatpassengers, they may now be found integrated into seats and door panelsfor side protection, and integrated into headliners, pillar trim andquarter panels for roll-over protection. Additional locations mayinclude air bags for knee protection by deploying from below theinstrument panel, or air bags built into the back of the front seats toprotect rear seated passengers, and even air bags integrated into theshoulder belts which are used for primary occupant protection.

For example, U.S. Pat. No. 6,102,435 to TRW Vehicle Safety Systems,Inc., entitled “Vehicle Headliner with Inflatable Side Curtain” isdirected at a headliner assembly including an inflatable vehicleoccupant protection device which is supported behind a door which hingesopen upon bag inflation. U.S. Pat. No. 5,540,459 to Ford Motor Company,entitled “Roof Rail Mounted Air Bag Assembly” is directed at aninflatable restraint device having a trim cover which deflects away atits lower edge when an air bag opens downward from the roof side railand between the occupant seat, the door and the window of the vehicle.U.S. Pat. No. 6,152,482 to Ford Global Technologies, Inc., entitled“Vehicle Inflatable Restraint System Trim with Trim Deploying Module” isdirected at an inflatable restraint module mounted longitudinallyadjacent a roof rail which when activated causes a flap member tooperatively force a headliner assembly over a pillar trim piece to routethe inflatable restraint past the pillar trim. U.S. Pat. No. 6,059,311to Breed Automotive Technologies, entitled “Pillar-Mounted Side Impactand Rollover Air Bag” is directed at a side impact and crash protectionand roll-over system comprising a web guide attachable to a pillar of avehicle, a seatbelt system and an air bag assembly stored adjacent theweb guide which when inflated is positioned adjacent the pillar. U.S.Pat. No. 5,531,470 to Joalto Design Inc., entitled “Side Air BagIncorporated in Vehicle Outer Armrest” is directed at a vehicle sideimpact air bag system wherein the air bag is located in an outboardarmrest which is pivotably attached to a vehicle seat. Upon deployment,a cover panel located over the armrest hinges along its bottom edge toallow the air bag to upwardly expand without restriction. These air bagsystems all include some sort of cover which is integrated into thesurrounding vehicle trim to prevent tampering with the air bag or themechanism that causes the air bag to deploy and which further hinges ordeflects to allow proper bag deployment. These covers generally comprisean outer cover skin and a rigid door substrate, sometimes separated by afoam layer.

As these safety devices have become accepted and more popular, it hasbecome common to conceal the presence of the air bag and its inflatingapparatus by providing a cover which is indistinguishable from thesurrounding plastic trim (commonly known as the invisible or hidden airbag door). Thus, the aesthetics of the interior are enhanced and thereminder of the presence of the safety equipment is minimized.

As the locations for the air bag systems have proliferated, the need fordifferent types of materials to cover the air bag systems andeconomically integrate into the surrounding interior trim package hasbeen recognized. Generally, in cars, the materials used above the “beltline” are desirably softer in surface hardness while below the “beltline” where scuffing is more prevalent, hard injection molded plasticsmay be more preferentially employed

Originally, air bag cover outer skins were of a soft thermoplastic(polyvinyl chloride, thermoplastic olefin or elastomer, thermoplasticurethane, etc.). Since seats, headliners, door panels and pillars areoften fabric covered, particularly in European cars, there has been arecent focus on developing fabric or textile materials as candidates forthe outer surface of air bag covers which might meet the demandingaesthetic and functional requirements.

One construction of a fabric covered air bag door that employs a “peelback” method is disclosed in. U.S. Pat. No. 6,050,595 commonly assignedto the assignee of the present invention. The '595 patent is directed atan air bag closure assembly comprising a trim member including a paneland a skin, wherein the skin is supported on the outer surface of thedoor and trim member panel and whereupon air bag inflation the frontedge of the door is pivoted away from the opening around the hinge toprovide a path for air bag deployment through the panel. The skin is atleast partially separable from at least a portion of the panel outersurface that extends laterally outward from the side edges of the doorand from the front edge of the door to a front edge of the skin adjacentthe front edge of the door, the skin delaminating when the door carriesthe skin outwardly and lifts the skin from the panel outer surface asthe air bag inflates and forces the door to an open position, the skinforming a skin tent over the door, the skin tent having a skin tentopening formed by the delaminated front edge of the skin thus providingan exit for the deploying air bag.

To provide deployment of the airbag without fragmentation of the coverand to ensure tearing of the cover skin and reliable opening of the airbag door in combination with concealment of the door and door opening,it has been found that pre-weakening of the cover skin in a pattern thatapproximates the air bag door opening is desired. This pre-weakening ishas been accomplished by reducing the cross-section (i.e. thickness) ofthe cover skin and door substrate locally to form a tear seam. This maybe accomplished by molding a groove into the door substrate and into theinside of the cover skin or by the use of a laser or knife to form agroove (slots, perforations, etc.) in the substrate layer which mayextend into a foam and/or cover layer.

For example, European Patent Application EP 1216894A1 to DelphiAutomotive, entitled “Instrument Panel with Integral Hidden Door Coverand Method of In-Process Manufacture Thereof” is directed at forming ascore on the backside of a preferably vacuum formed instrument panelskin with a cylinder-activated blade to create a weakened region in thepattern of an air bag door seam. The skin is then foamed in place with aretainer. U.S. Pat. Nos. 5,421,608; 5,431,435; 5,447,328/RE 37,540;5,564,731; 5,685,930; 5,783,016; 5,804,121; 5,902,428; 5,941,558;5,961,143; 5,975,563; 6,050,595; 6,131,945; 6,203,056; 6,402,189;6,457,738; 6,460,880; and U.S. application Ser. Nos. 10/286,251;60/367,924; 60/368,418; and 60/411,548; commonly assigned to theassignee of the present invention and included herein by reference, aredirected at air bag doors which are contained in or molded as part of alarger panel and which contain weakened areas to allow predictabledeployment of an air bag through the panel.

While examples of this technology are common with the flexible skinmaterials, it has not been fully demonstrated that weakening of a fabriclayer for a cover can be similarly accomplished. Use of a laser beam tocut fabric is known. U.S. Pat. No. 6,283,001 B1, entitled “Facility forCutting Fabric . . . ” recites “in a preferred embodiment, the cuttinghead is a laser cutting beam. This type of cutting head possesses alaser beam source and a corresponding focusing optical system, whichfocuses the laser beam on the fabric band. To avoid undesirableoxidation, an additional protective gas jet can be provided, whichpushes away from the cutting position the oxygen containing air by meansof inert gases, i.e.: nitrogen or other inactive gases. Especially,where artificial fiber containing textiles are concerned, a fume removalsystem can be provided, which, during the cutting, removes the vaporizedsubstance in order to uphold the required working place environmentalregulations (MAK-values). Attention is also directed to U.S. Pat. No.6,140,602, entitled “Marking of Fabrics and Other Materials Using ALaser” to Technolines LLC, which discloses a method for imparting laserinduced patterns and other designs on thin fabrics and leathers.

Regarding specific references to weakening cover layers in air bag doorsystems, U.S. Pat. Nos. 6,294,124 B1 and 5,744,776 to Bauer of TIPEngineering suggest the use of a laser to weaken the backside of a“cover layer” by cutting through the substrate and partially through thecover layer. FIG. 13 therein is said to illustrate “the use of a laserapplied to a cosmetic cover layer 92 shown as a textile material asmight be used with a side impact air bag system, which has a scrimbacking layer 94 bonded thereto. The laser scored groove 95 penetratescompletely through the backing scrim 94 and partially through thetextile layer 92.” Published United States Application No. 20022/0050046A1 also to TIP Engineering, is entitled “Process for Manufacturing anAutomotive Trim Piece Preweakened To Form An Air Bag DeploymentOpening”. This application recites a process for constructing a trimpiece having a section pre-weakened in a pattern to allow formation ofone or more deployment doors, whereby a stiff substrate is formed havingone or more integral doors with a predetermined gap between adjacentportions and one or more cover layers are laid over the substrate paneland extend across the predetermined gaps. Pre-weakening of theoverlaying cover layers is accomplished by laser scoring portions of theinside of the cover layers along the gap.

Therefore, while the field not surprisingly has many disclosurescharting off in a variety of different directions to provide acosmetically appealing and functional air bag deployment system, therestill exists a need in the art for fabric or textile covered trim panelsto be used as air bag covers, wherein the fabric as well as thesubstrate is efficiently pre-weakened to allow predictable deployment ofthe air bag and tearing of outer cover layer.

SUMMARY OF THE INVENTION

According to the present invention, an air bag cover for an air bagsystem in a motor vehicle is provided having a textile or fabric outerlayer which has been pre-weakened in a pattern to allow a predictabledeployment of the air bag. The air bag cover preferably comprises anouter textile or fabric layer, a backing layer and a plastic substrate,preferably formed by low pressure molding. The pre-weakening may beaccomplished by reducing the cross-section of some or all of the layersof the air bag cover from at least one of the front and back side of thecover. Alternatively, the pre-weakening may be accomplished by weakeningthe fibers or yarn used in the outer layer by, e.g., laser, chemicaltreatment, or by photodegradation, or by melting or by actually weavinga pattern into the fabric, the pattern comprising weaker yarns which arestrategically positioned to provide an area which is weaker than theremainder of the fabric and which preferentially tear upon air bagdeployment. In addition, in the case of laser, e.g., the inventionherein weakens the fabric without a physical alteration wherein, e.g.,the thickness and/or appearance of the fabric remains substantiallyunchanged by a controlled laser exposure.

According to another aspect of the present invention, air bag covershaving a fabric outer layer are provided that can be used anywhere inthe interior of the vehicle to complement the appearance of thesurrounding interior trim, including but not limited to, the instrumentpanel, steering wheel, console, door panels, seats, headliner, quarterpanels, pillars and window trim.

According to another aspect of the present invention, a preferredconstruction for fabric covered air bag covers is provided whichincludes a fabric or textile layer, a backing layer and a lowpressure-molded substrate.

According to another aspect of the present invention, a means forpre-weakening the fabric or textile outer layer of the air bag cover isprovided by reducing the cross-sectional thickness of the outer layerlocally with a laser or a knife blade from at least one of the front andback sides of the outer layer.

According to another aspect of the present invention, a means forpre-weakening the fabric or textile outer layer of the air bag cover isprovided by weaving into the fabric outer layer a pattern correspondingto the shape of the air bag door opening, the pattern comprising yarnthat is weakened to a lesser tensile strength than the remainder of theyarn used in that area.

According to another aspect of the present invention, the fabric outerlayer of an air bag cover is weakened by treating the fabric locallyfrom at least one of the front and back sides with a chemical, with alight source causing photodegradation, or with a laser.

According to another aspect of the present invention, an air bag coverfor an air bag safety system for a vehicle is provided, comprising afabric outer layer having a front side and a backside, and comprising aweakened portion and a non-weakened portion. A substrate containing anopening is provided, said opening having a periphery, the substratepreferably formed by low pressure molding. The fabric outer layer ismade to overlie the opening in the substrate, and the non-weakenedportion of said fabric layer is made to overlie a portion of saidperiphery and said weakened portion overlies another portion of saidperiphery.

According to yet another embodiment of the present invention, an air bagcover for an air bag safety system for a vehicle is provided, comprisinga fabric outer layer having a front side and a backside, and comprisinga reinforced portion and non-reinforced portion. A substrate containingan opening is provided, said opening having a periphery, the substratepreferably formed by low pressure molding. The fabric outer layeroverlies the opening in the substrate, and the reinforced portion ofsaid fabric layer overlies a portion of said periphery.

These and other objects, features and advantages of the presentinvention will be understood through consideration of the followingdetailed description in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an air bag cover assembly constructedaccording to the present invention and integrated into a vehicleinstrument panel.

FIG. 2 is a cross-sectional side view of an air bag deployment assemblydisposed behind the air bag cover assembly and instrument panel of FIG.1 taken along lines 2-2. FIG. 3 is a magnified fragmentarycross-sectional view of an air bag cover assembly constructed accordingto the present invention.

FIG. 4 is a magnified fragmentary cross-sectional view of an air bagcover assembly constructed according to the present invention with analternate weakening pattern.

FIG. 5 is a magnified fragmentary cross-sectional view of an air bagcover assembly constructed according to the present invention with analternate weakening pattern.

FIG. 6 is a simplified flow chart illustrating the steps of molding afabric covered trim panel according to the present invention.

FIG. 7 is a cross-sectional view of a molding apparatus containing a lowpressure molded trim panel with a fabric layer and backing layer bondedthereto.

FIG. 8 is a magnified fragmentary cross-sectional view of an air bagcover constructed according to the present invention illustrating analternate embodiment.

FIG. 9 is a magnified fragmentary cross-sectional view of an air bagcover constructed according to the present invention illustrating withan alternate weakening pattern of the second embodiment.

FIG. 10 is a magnified fragmentary cross-sectional view of an air bagcover constructed according to the present invention illustrating analternate weakening pattern of the second embodiment.

FIG. 11 is a cross-sectional view of the molding apparatus of the trimpanel of FIG. 10.

FIG. 12 is a diagrammatic view showing a third embodiment for preparinga tear seam according to the present invention.

FIG. 13 is a view taken along lines 13-13 of FIG. 14.

FIG. 14 is a diagrammatic view showing an alternate method of preparinga tear seam according to the third embodiment of the present invention.

FIGS. 15 and 15A are enlarged diagrammatic views of two differentconstructions of the third embodiment of the present invention havingyarn of different strengths.

FIG. 16 is a sectional view of FIG. 15.

FIG. 17 is a diagrammatic view of one pattern of weaker yarns includedin a fabric layer.

FIG. 18 is a diagrammatic view of an alternate pattern of weaker yarnincluded in a fabric layer.

FIG. 19 is a schematic illustrating the orientation of the tensile andelongation samples cut from the laser treated fabric according to thepresent invention.

FIG. 20 is a diagrammatic view of a laser used to weaken a fabric layeraccording to the present invention.

FIG. 21 is a magnified fragmentary cross-sectional view, similar to FIG.2 of an alternative air bag cover assembly constructed according to thepresent invention.

FIG. 22 is an enlarged diagrammatic view of a construction an exemplarywoven fabric layer consistent with the present invention having yarn ofdifferent strengths.

FIG. 23 is a sectional view of the fabric construction of FIG. 22.

FIG. 24 an enlarged diagrammatic view of a construction an exemplaryknitted fabric layer consistent with the present invention having yarnof different strengths

In the appended drawings, common elements use the same numericcharacters but are distinguished by the addition of a letter to identifya common element between embodiments (for instance, 10 10A, 10B, etc.).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1, a fabric covered automobile instrument panel assembly 10 isshown as would be installed below the windshield in the cockpit of avehicle. An inflatable restraint assembly or air bag system (not shown)for protecting the occupants of the vehicle is located beneath anintegrally formed air bag door 14, the door having a perimeter defined,in part, by a hidden marginal edge 16, shown by the dashed lines. Theperimeter 16 may also be defined as the lateral boundary of the door 14,the door 14 being defined as that portion of the integrally formed panel12 and door 14 that is separable or bendable from the panel 12 under theforce of air bag inflation. The door 14 and vehicle instrument panel 12may be integrally formed as a single unitary piece. Pre-weakening of thepanel 12 to demarcate the air bag door 14, usually from the backside topreserve an uninterrupted Class A outer surface may take place along oradjacent the perimeter 16.

The automobile instrument panel assembly generally shown at 10 in FIG.1, represents a first preferred embodiment of the present invention.FIG. 1 shows a fabric covered air bag door 14 integrated into thepassenger side of a fabric covered automobile dashboard or instrumentpanel 12. Alternatively, the air bag cover may be integrated into theknee bolster area 30, steering wheel hub 40, or other areas in theinterior of the vehicle including, but not limited to, seats, headliner,pillar trim, door panels, quarter panels, roof rails (all not shown) andthe like.

The assembly 10 comprises a trim panel generally indicated at 12 in FIG.2 and an integral air bag door, generally indicated at 14. The air bagdoor 14 may be molded as part of the trim panel 12 and is disposed inand closes a like-shaped air bag deployment opening 28 in the trim panel12. The door 14 has an outer edge 16, which abuts and forms a frangibletear seam 26 with an inner edge 22 of the air bag deployment opening 28.The seam 26 formed in the substrate 20 may comprise an area of reducedcross-section created by molding the section thinner than the thicknessof the surrounding substrate during the low pressure molding processthat forms the panel 12 and door 14 and back-fills the outer surfacelayer 32. Alternatively, the seam 26 may be formed by routing, lasercutting or knife cutting into or through the substrate. The seam may bea continuous groove or intermittent slots or perforations formedpartially through or completely through the substrate layer 20. The tearseam 26 is preferably invisible to the occupants of the vehicle forreasons of aesthetics, and thus is shown in FIG. 1 by dashed lines.Alternatively, the weakened area or tear seam 26 may be formed in thetop Class A surface of the panel, or alternately in both the top andbottom surfaces of the molded panel. The panel 12 is generally molded ofa somewhat ductile plastic and the frangible tear seam 26 of reducedcross-section is designed to fracture due to the pressure of theinflating air bag, allowing the air bag door 14 to break loose from theinstrument panel 12 predictably and without fragmentation.

As shown in sectional view in FIG. 2, taken at line 2-2 of FIG. 1looking in the direction of the arrows, a fabric covered instrumentpanel 12 covers an air bag system 18 that is located behind theinstrument panel directly beneath the air bag door 14 and is mounted toa metal portion of the vehicle structure (not shown). The air bag systemincludes an inflatable folded air bag 22, an inflator 24, canister 25and an impact sensor (not shown) that on vehicle impact triggersignition of the inflator to inflate the air bag for deployment into thepassenger space directly in front of a passenger seated on that side ofthe vehicle. As further shown in FIG. 2, a plastic deployment chute 51is attached at 44, preferably via vibration welding, to the backside ofthe instrument panel substrate 20 just outboard of the frangible tearseam 26 in the area of the air bag door 14 to direct the air bag 22 andwhich creates sufficient structure in the panel to direct the force ofthe inflating bag into the pre-weakened tear seam 26 surrounding the airbag door 14. A reaction plate 52 which contains stiffening ribs 46 issimilarly and preferably welded at 48 to the air bag door 14 backside toprovide stiffness. The deployment chute and reaction plate arepreferably molded of a plastic compatible with the instrument panelsubstrate 20 and are welded to the backside of the instrument panelsubstrate 20 and door 14 so that the tear seam 26 is located in linewith the chute inner periphery 53. The reaction plate 52 is attached tothe air bag door portion 14 of the molded hard instrument panel 12 suchthat on air bag deployment the welded air bag door/reaction platecombination separates from the instrument panel/deployment chute weldedassembly. As the air bag 22 expands to fill the area inside thedeployment chute 51, the bag contacts the reaction plate 52 and forcesthe welded reaction plate 52/air bag door 14 to fracture at the tearseam 26.

Various plastic materials may be molded to form both the instrumentpanel with integral air bag door and the deployment chute/reaction plateincluding, but not limited to, acrylonitrile-butadiene-styrene,polycarbonate, polyurethane, polyarnide, styrene maleic anhydride,polypropylene, polyolefin, thermoplastic olefin, thermoplasticelastomer, polyphenylene oxide and combinations thereof.

As alluded to above, the attachment of the reaction plate and deploymentchute is preferably by vibration welding of the molded chute/plate tothe instrument panel but may also comprise other welding methods andattachment means including, but not limited to, hot plate welding,adhesive mechanical attachment, etc.

As shown in FIG. 2, a metal tether 41 which may contain a formed loop 80is attached to the reaction plate 52 by a rivet 60 and washer 64 and tothe deployment chute 51 by a fastener 56 screwed into a boss 54. Thewasher 64 may be an H-shaped piece of stock that fits between the ribsof the reaction plate. The metal tether 41 may be a steel stampingformed to shape and alternatively may comprise a series of holes orslots in the stamping in the area of the loop 80 to assist in hinging ofthe tether to control air bag door 14/reaction plate 52 travel. Theformed loop 80 may comprise one or more loops disposed between thereaction plate 52 and the deployment chute 51 to create the desiredamount of slack for the deploying door. In addition, the loop itself maybe selectively positioned at the open space under the area of reducedcross-section 26 as shown at 81. Alternatively, the loop may beselectively positioned adjacent the fastener 56. Typically, the tethermay be one or more metal stampings approximately 200 mm wide by 0.6 mmin thickness. Preferably, the tether may be the same width as thereaction plate to provide a predictable deployment result at hightemperature and extend through a bent section 81 to be anchored at thedeployment chute. Alternatively, the metal tether 41 may not include aloop 80 and may act as a hinge for the door 14.

The instrument panel 12 further comprises an outer layer of fabric 32and may further include a backing layer 34. As will be shown infragmentary cross-section in FIG. 3, the outer layer of fabric 32 andthe backing layer 34 may be weakened in the area of the door seam 26 toprovide predictable and reliable deployment of the air bag 22 throughthe opening 28 in the trim panel 12.

Turning to FIG. 3, a preferred embodiment of the construction of thepre-weakened fabric covered air bag door and instrument panel assemblyis shown. This enlarged fragmentary cross-sectional view is taken fromFIG. 1 at the circle indicated by the numeral 3 showing the detail ofthe tear seam 26 in the substrate 20 and additional weakening of thecover layer 32 and backing layer 34. A tear seam 36 extends through thebacking layer 34 and partially through the fabric layer 32 to providepredictable tearing of the cover layers 32, 34 during air bagdeployment. The cover layer tear seam 36 is preferably located justoutboard of the door/substrate tear seam 26 so that the mode of failurefor the cover layers 32, 34 is in tensile rather than in shear, as thisprovides more consistent tearing. Alternatively, the cover layer tearseam 36 may be aligned over the door/substrate tear seam 26. (See FIG.4.) Both tear seams 26, 36 may extend around the full periphery of thedoor 14 or may be interrupted. In addition, in terms of specificdimensions, the outboard cover layer tear seam 36 may be outboard of thedoor/substrate tear seam 26 by an amount equal to or greater than 1.0mm, and can lie in the range of 1.0 mm to 50 mm, and at any 0.1 mmincrement therebetween. Most preferred values are in the range of 5.0 mmto 15.0 mm.

Manufacture of the fabric covered instrument panel with integral air bagdoor and pre-weakened tear seams may be preferably accomplished asfollows. A fabric material 32 is chosen which will withstand the rigorsof the area in the vehicle in which it will be used (abrasion, heat,light exposure, feel, appearance, etc.). The fabric may include, but isnot limited to, cloth, carpet, knit, tricot, chenille, natural orsynthetic composition, woven or non-woven, in a thickness, weight anddenier which meets the requirements for a trim material in the area ofthe interior of the vehicle that will house the air bag.

Flat fabrics are preferred in this invention, either knits or wovens. Asused herein, the term “woven fabric” refers to a fabric containing astructure of fibers, filaments or yarns which are orderly arranged in aninterengaged fashion. Woven fabrics typically contain interengaged yarnsin a “warp” and “fill” direction. The warp direction corresponds to thelength of the fabric while the fill direction corresponds to the widthof the fabric. Suitable pile or effect yarns for use in the presentinvention include, but are not limited to, natural fibers such ascotton, linen, jute, hemp, cotton, wool, and wood pulp, regeneratedcellulosic fibers such as viscose rayon and cuprammonium rayon, modifiedcellulosic fibers such as cellulose acetate, and synthetic fibers suchas those derived from polypropylene, polyethylene, polyvinyl alcohol,polyesters, polyarnides, and polyacrylics. The above-mentioned pile oreffect yarns may be used alone or in combination with one another.Multicomponent fibers comprising a blend of one or more of the abovematerials may also be used if so desired. Preferably, the cover fabriccomprises a polyester woven fabric having a weight of about 300-350grams/square meter, although weights as low as 100 gr/m² have been used.Further, knits seem to perform equally well.

A backing material 34 may be optionally applied to the underside of thefabric to prevent strike-through by the subsequent substrate 20 when itis molded behind the backing layer. The backing material serves toreduce the porosity of the fabric layer and is preferably a non-wovenlayer of polyester or polypropylene with a weight of about 200-250grams/square meter. The backing material may include, but is not limitedto, a spun laced non-woven, a needle punched non-woven, felt, anadhesive layer, and a plastic backing layer such as EVOH, EVA,polyethylene, and polyester acrylic. The backing layer 34 may beattached to the underside of the fabric layer 32 by methods including,but not limited to, flamebonding, adhesive film, adhesive spray, etc.Alternatively, the fabric outer layer 32 and backing layer 34 may beseparated by a foam layer to provide a softer touch for the trim paneland air bag cover.

The composite fabric layer 32/backing layer 34 is then preferablypre-weakened in a pattern roughly coinciding with the outline of the airbag door area 16. Pre-weakening may be accomplished by laser scoring, bysonic knife or by the application of a hot knife blade under pressurewhich melts through the backing 34 and partially through the fabriclayer 32. This is done to provide an uninterrupted surface over the airbag door area and provide a hidden air bag door 14 in the panel 12. Thepre-weakened tear seam 36 in the cover layers 32, 34 may comprise acontinuous groove or may be a series of intermittent slots or holeswhich provide weakening.

In a process which is particularly suitable for use in molding anarticle with fabric covering, as shown in sectional view in FIG. 7,coacting members are provided for in injection molding machine, one ofthe members having a cavity portion associated therewith with aconfiguration of one side of the article to be molded, while the otherof the two members has a detail portion that projects therefrom into thecavity portion of the other member when the two members are broughttogether along a parting line. The fabric sheet is interposed betweenthe two members along the parting line and may be positioned inregistration with the cavity by way of a robotic arm, carrier plate ormotorized drive assembly that is able to position the fabric accurately.A substrate layer 20 is then formed behind the backing layer by a lowpressure molding process such that the fabric layer becomes the “skin”of the molded article. This is shown in FIG. 7 wherein a fabric coverlayer 32 and backing layer 34 containing a pre-weakened tear seam 36 aredisposed between an injection mold cavity 50 and core member 60 andback-filled with a plastic to form a substrate 20 filling in any openspace between mold cavity 50 and core 60 and urging the cover layer 32and backing layer 34 to conform to the inner surface 58 of mold cavity50.

Low pressure molding processes are preferred herein for forming fabriccovered trim panels according to the present invention as they typicallyresult in less disruption to the cover layers during manufacture(stretch, wrinkling, compression, overheating, etc.) and are moreeconomical for producing large parts. Low pressure processes that aresuitable for this invention generally are of two types, thermoset andthermoplastic. The thermoset low pressure molding processes aregenerally liquid processes, often called reaction injection molding(RIM) where a reactive polymer or its precursors are injected into aclosed mold and flow to fill the open space between mold halves beforesolidifying. The types of polymers may include, but are not limited to,urethane, polyester, dicyclopentadiene, polyurea, epoxy and acrylic, andmay include fillers and reinforcements.

Low pressure thermoplastic molding processes generally entail lowerclamp pressure (in the order of 1000 psi) than regular injection moldingprocesses due to one or more of the following characteristics:

-   -   filling the mold while it is partially open,    -   use of cascading sequential gating to distribute the flow,    -   pre-expanding the melt,    -   introducing a gas to fill out a short shot,    -   low speed injection of the polymer,    -   elimination of pack out and hold pressure,    -   use of easy flow, low melt viscosity, and high melt index        polymers.

Examples of low pressure molding processes include the MuCell processwhere carbon dioxide or nitrogen is injected in a supercritical fluidstate into the injection molding machine barrel to form a single phasesolution which when injected into a mold, expands into fine bubbleswhich fill the mold, and a gas assist process, such as the Gain process,where the injection mold is filled with less plastic than is required tomold a solid part, and a gas under pressure is introduced into the meltwhich expands to fill out the cavity. Ube Corp.'s Dieprest processinjects polymer melt into a partially open tool, then closes the tool(injection-compression) to fill out the cavity. The mold may later beopened to reduce damage to the cover layer. Sumitomo Corp. and Van DornCorp. provide a series of cascading sequentially activating valve gatesin a hot runner control system that distribute the polymer around themold, reducing flow distance and providing a more consistent meltvelocity. Alternatively, the polymer melt may be extruded across thecavity of the mold using an X, Y, Z robot. Also, near-final-shapepreforms may be provided which are placed between the mold halves andrequire little flow to fill out the open space when the mold is closed.

As therefore alluded to above, in a preferred embodiment, the coverlayers 32, 34 containing a pre-weakened seam 36 are placed betweencoacting mold halves and a polymer melt injected using cascading,sequentially activated gates distributed across the mold. FIG. 6 brieflydescribes this process. This process involves the sequential injectionof polymer melt into the mold such that the mold is sequentially filledaccording to each sequential injection of material. Each sequentialinjection is therefore capable of relatively low injection pressuressince it is unnecessary to fill the entirety of the cavity via use of asingle gate. In addition the flow distance for fill-out of each sectionof the mold corresponding to the sequential gates is less than for theentire mold cavity. Accordingly, as used herein, the term sequentiallyactivated gates defines that situation wherein a plurality of gates areemployed, connected to the mold cavity, to distribute the moltenmaterial throughout the mold cavity. In that context, the gates, whilepreferentially operating in sequential format, may include some degreeof overlap in their filling sequence.

In accordance with the present invention, the preweakening of the fabricand backing present several options. Specifically, one can firstpreweaken the fabric and place the backing on the fabric, position suchfabric/backing in the mold, wherein the backing prevents flow-throughduring the ensuing step of low pressure molding and substrate formation.This is followed by weakening (laser, cutting, etc) through thesubstrate and partially into the backing material. Optionally, one canpreweaken both the fabric and backing simultaneously, followed by lowpressure molding and substrate formation. Specifically, in this lateroption, it has been recognized that low pressure molding does not exertas much pressure against the preweakened fabric/backing cover layer, inwhich case the lack of backing at the preweakened sections of thefabric/backing cover layer do not become a significant issue

The thermoplastic polymers used to form the substrate of the presentinvention may include, but are not limited to, polypropylene,polyethylene, polycarbonate, acrylonitrite-butadiene-styrene,polyphenylene oxide, acrylonitrile-styrene-acrylic, styrene maleicanhydride, thermoplastic elastomers, thermoplastic olefins and blendsand alloys thereof, optionally including fillers and reinforcements.

Relatively flat trim panels which are used as air bag covers can beformed using the above-described process, as the flow of the polymermelt urges the cover layer into intimate contact with the mold cavity.Deeper panels having more complex shapes may require the preforming ofthe cover layers 32, 34 prior to backfilling with polymer to form thesubstrate 20.

This preforming of the cover layers can occur in a separate male orfemale vacuum forming apparatus or may take place in the cavity of theinjection mold using a porous mold and pressure assist.

As can be seen in FIG. 2, once the fabric covered trim panel has beenformed in the injection mold, it is removed and the tear seam 26 isformed to demarcate the air bag door 14 from the panel 12. The tear seam26 in the substrate 20 may be formed by a number of known processesincluding, but not limited to, laser scoring, sonic knife, heated knifeor by forming the seam as part of the injection molding process throughthe inclusion of sharp mold segments (blades) in the mold core whichproject through the substrate and are encapsulated by the flow of thepolymer around these blades. The tear seam 26 may be a groove,intermittent through-slots or through-holes.

FIG. 4 illustrates an alternate pattern of weakening wherein the fabriccover layer 32, the backing layer 34 and the substrate 20 may all bepre-weakened by laser, knife, etc. in a single operation after the trimpanel has been molded. In this embodiment, the cover layer 32 andbacking layer 34 are not scored, thinned or pre-weakened prior to thelow pressure molding process, but rather after the panel has beenformed. The pre-weakening may be in the form of a groove, slots or holesthat do not extend through the Class A (outer) surface of the trim panelbut may extend into any one or all of the cover layers or substrate.

As alluded to above, FIG. 5 illustrates another pattern of weakeningwherein the fabric cover layer 32 is first pre-weakened to form a tearseam 36′ followed by application of the backing layer 34. Subsequently,the cover layer 32/backing layer 34 are formed to the mold cavity by alow pressure injection molding process to form the substrate 20. Uponremoval from the mold, the substrate 20 and backing layer 34 arepre-weakened by laser or knife to form tear seam 26, 36 withoutpenetrating the cover layer 32. In this embodiment, pre-weakening of thebacking layer may be accomplished by fully penetrating the backinglayer, as shown in FIG. 5, or by partial penetration into the backinglayer. In addition, by offsetting the location of the tear seams 26 and36 from 36′, strike-through of the molten polymer forming the substrate20 into the cover layer 32 is minimized.

An alternate construction for a hidden tear seam on a fabric coveredtrim panel comprises adhering a backing layer 34 to a fabric cover layer32 and pre-weakening the resultant laminate with a laser or knife fromthe backside to form a tear seam in a desired location. In thisembodiment, the initial pre-weakening would preferably fully penetratethe backing layer 34 and only partially penetrate the fabric cover layer32. Such pre-weakening seam may be in the form of a groove, slots orholes. The thus pre-weakened laminate may then be pressure or vacuumformed over a plastic substrate formed by low pressure molding andcoated with an adhesive. The thusly formed trim panel may be thenpre-weakened by laser, knife or other means, from the backside todemarcate an air bag door 14 from the remainder of the panel 12. Thepre-weakening or scoring in this embodiment would only penetrate throughthe substrate layer 20 and may comprise a groove, slots or holes, andmay be offset from the pre-weakening in the backing layer and fabriclayer.

A still further construction of the present invention for providingfabric covered air bag covers for vehicles employs the use of apre-weakened cover layer without the use of a substrate. The presentinvention therefore includes a cover assembly for concealing an air bagrestraint system, the assembly comprising a frame defining an air bagopening, a fabric covering attached to the frame in a taut manner, thefabric covering having a single tear seam that is ruptured when thefabric covering is impacted by the inflating air bag, which maypreferably form an elliptical opening for deployment of the air bag intothe passenger compartment, the tear seam, preferably being cornerlessand having ends spaced from the frame. According to this embodiment thefabric covering may also be adhered to a backing layer, either of whichis pre-weakened according to the present invention to form a tear seam.

It is further possible with any of the aforementioned examples toprovide a backing layer only locally covering the area where the fabrichas been weakened to prevent strike through.

Weakening the Fabric Layer from the Front Side

An alternate embodiment of the present invention for providing a fabriccovered automotive trim panel for covering an air bag system may includepre-weakening the fabric outer layer from the outer surface or class Aside of the panel. The result will be a panel having an interruption orvisible evidence of the weakening. U.S. Pat. No. 5,131,678 commonlyassigned to the assignee of the present invention and included herein byreference is directed at a decorative panel concealing a storagecompartment for an inflatable air bag, comprising a backing plate havinga U-shape outline forming the storage compartment and defining a doorhaving a hinge line extending between the ends of the cut line, an innerlayer of foam, an outer skin layer forming the outer surface of thepanel and having a peripheral groove outlining the door, the groovebeing characterized by two spaced side walls extending from the outersurface inwardly of said foam and each of said spaced side walls havingend portions thereon completely separated by a slit cut therebetween,said spaced sidewalls extending downwardly so as to cause said slit tobe located at a point which is not visually observable from the outersurface of the panel to create a tear seam along the weakened section sothat inflation of the air bag will force the door to separate saidspaced side walls and enable deployment of the air bag outwardly fromthe panel.

An improvement upon this invention is shown is FIG. 8. In thisembodiment, a trim panel has been molded with a fabric outer layer 32Aand containing a groove or style line 44 that indicates the approximatelocation of the edge of the integral air bag door 14A formed in thepanel. To pre-weaken the outer layer of fabric 32A and providepredictable tearing of the outer layer, a laser or knife is used to cutthrough the fabric layer 32A at the bottom of the groove or style line44. The depth of the groove serves to hide the presence of the tear seam46 cut into the fabric. The substrate 20A may be scored partially fromthe front side in the same operation that weakens the fabric layer 32Aor the substrate 20A may be scored from the backside using any of themethods as described herein (as noted at 26A by the dashed lines). Inthis embodiment it may not be necessary to provide a backing layerbehind the fabric outer layer 32A as the fabric has not been locallythinned prior to backfilling by low pressure injection, andstrike-through will be less likely. A method for forming a tear seamwith a knife as described in U.S. Application 60/411,548 which iscommonly assigned to the assignee of the present invention may be usedand is included herein by reference.

In a related embodiment, the fabric layer 32A may be removed from thedoor area 14A to provide a design contrast and a visible air bag door.The present invention is therefore directed at a method of manufacturingan instrument panel assembly of an automotive vehicle having an integralair bag deployment door, said method comprising the steps of lowpressure molding a retainer of rigid plastic material having a main bodyportion, an air bag deployment door portion and a molded-in channelextending into the retainer from an outer surface thereofinterconnecting the main body and door portion and defining a tear seamline for the door portion, preparing a cover comprising an outer layerof woven or knitted fabric, applying an adhesive to the outer surface ofat least the main body portion of the retainer, positioning the woven orknitted fabric over the outer surface of the retainer and drawing avacuum on the retainer to urge the woven or knitted fabric against themain body and door portion of the retainer and down into the channel,and severing the woven or knitted fabric within the channel.

In an alternate construction of this embodiment, providing a witnessline on the front surface of a fabric covered trim panel is accomplishedby using a hot die that forms the weakened seam area. FIG. 9 illustratesa fabric outer layer 32A backed by a barrier layer 34A into which a hotdie 70 has been pressed in the direction of Arrow B to reduce thethickness of the fabric layer 32A and weaken the fabric by melting andsevering some of the fibers. The reduction in thickness 66 may be in adecorative design or pattern, a portion of which essentially coincideswith an edge of the air bag door. The barrier layer 34A is present toprevent strike-through during application of the hot die and like thebacking layer in previous embodiments, to prevent strike-through of thepolymer melt during subsequent backfilling using a low pressure moldingprocess. In this embodiment, weakening of the substrate 20A and backinglayer 34A may be accomplished after molding by laser or knife cuttingfrom the back side to form a tear seam 26A adjacent to or in line withthe thinned fabric area 66. This weakening may penetrate through thesubstrate 20A in a groove, slot or hole pattern and may penetratepartially or fully through the backing layer 34A.

A still further construction for forming a visible tear seam in a fabriccovered trim panel utilizes blade-like projections in the injection moldcavity as shown in sectional view in FIG. 11. Here, coacting members ofa low pressure injection mold are indicated at 60A for a core member andat 50A for a cavity member. This sectional view of the mold apparatusfurther illustrates a blade member 70 projecting from a portion of thecavity member 50A, the blade member 70 demarcating at least a portion ofan air bag door from a trim panel. A cover sheet comprising a fabriccover layer 32A and a backing layer 34A is preformed to include a groove72 which matches the blade member 70. The preformed sheet is then placedinto the cavity 50A of the injection mold and the groove 72 registeredto the blade member 70. The remainder of the open space between the coremember 60A and cavity member 50A is filled with polymer using a lowpressure molding process to form a substrate 20A. The blade member 70urges the cover sheet into contact with a depression 74 in the mold core60A, sealing the substrate 20A from forming therein and extending theformed cover sheet beyond the back surface of the substrate 20A. Theresultant trim panel 12A is removed from the injection mold and theportion of the cover sheet extending through the trim panel is cut offto form a weakened area in the area of the air bag door peripheral edge.This is illustrated in FIG. 10 where the cover sheet comprising fabriclayer 32A and backing layer 34A and extending through the substrate isindicated by dashed lines as being removed. The blade member 70 wouldpreferably have a stepped or perforated edge such that the cover sheetprojects through the substrate layer 20A in an intermittent pattern andleaves the door portion 14A connected to the trim panel portion 12A.

Alternatively, a backing layer 34A may not be required and only a fabriccover layer 32A comprises the cover sheet. Further, the blade member 70may comprise a series of flat projections or rods that project from themold cavity 60 surface and register with the preformed cover sheet toform a weakened pattern approximating the door 14A shape. The severingof the cover sheet extending through the substrate may also beaccomplished through the use of a laser or knife programmed to cut fromthe front surface of the panel into the groove 72 and through the coverlayer 32A and backing layer 34A.

Weakening the Fabric Internally

Yet another embodiment for pre-weakening a fabric layer to be used as anouter surface layer for an air bag cover for a motor vehicle interior,in addition to thinning, cutting or melting the fabric from either thefront (class A surface) or backside, involves the use of weaker fibersin the fabric. This may be accomplished by chemical treatment, byexposure to a radiation (heat or light) source or by weaving or knittingthe fabric using weaker fibers in a specific pattern over the air bagdoor to cause preferential tearing of the fabric upon the air bagdeployment. The chemical or radiation weakening embodiments may becarried out on a unformed or formed blank cut to size for use as a trimpanel with the weakening applied to a local area in a pattern over theair bag door. All of these fabric weakening embodiments describedhereafter may also be carried out on roll goods as part of themanufacturing process for the fabric and may extend fully across theroll to simplify manufacture or encompass the full surface of the door.

In a one construction, the fabric outer layer may be masked off andexposed to a photodegradation process whereby a beam of light isprojected on the front or back surface of the fabric in the area whichwill become the cover layer for the air bag door. Similarly, thetreatment may be in a discrete pattern (letter, shape, etc.) or may beaccomplished on roll goods as they are being manufactured, preferablywith the treatment extending across the width of the roll formanufacturing efficiency. Either the chemical treatment or photodegradation process may also be carried out on roll goods to treat thesurface in a discrete pattern much like color printing of the fabric isaccomplished. Broadly, this embodiment of the present invention involvestreating the air bag cover fabric 32B in the area that is to function asthe tear seam, i.e., the tear seam region 16B, from either the front orback surface of the air bag cover fabric 32B sufficiently to locallyweaken the material and produce a visibly undetectable tear seam 36B.FIG. 12 illustrates one method of generating the tear seam 36B accordingto this invention. A UV radiation device, or “UV generator” 48, isarranged over the one surface of the air bag cover fabric 32B andenergized to direct UV radiation 40 onto the facing surface of the coverfabric 32B. A UV blocking template 82 is arranged between the UVgenerator 48 and the cover fabric 32 to block the transmission of the UVradiation 40 to a non-tear seam region 84 of the air bag cover fabric32B except through prescribed openings 86 in the template 82. Theopenings 86 correspond in size and shape to the tear seam 36B to beproduced, i.e., the tear seam region 16B of the air bag cover fabric32B. As illustrated, the template openings 86 and tear seam region 16Bhave a corresponding U-shape, but this is just one pattern of manydifferent patterns that can be employed. Other patterns contemplatedinclude, but are not limited to, “X”, “C”, “H” and “I”-shaped tear seampatterns that roughly correspond to the outline of the air bag door 14B.The template 82 may comprise a panel made of metal, wood or othermaterial that would serve to block UV radiation transmission to theunderlying non-tear seam region 84 of the air bag cover fabric 32B whileallowing UV radiation transmission through the template opening 86 tothe air bag cover skin tear seam region 16B. The photodegradation of theexposed fabric material 32B can be controlled by controlling the UVexposure time. The time required to achieve a certain degree of materialdegradation may vary from one fabric to another and may depend on suchfactors as the type of fabric used for the cover, its thickness, theambient temperature, the intensity of the UV light, and the irradianceand wavelength of the light. The UV light employed preferably has awavelength in the approximate range of 10-340 nm to provide optimumenergy. It is also preferable that the UV light generator does not emitUV light outside this preferred range. More preferably, the UV generator48 emits no electromagnetic radiation in the infrared portion of theelectromagnetic spectrum in order to minimize or eliminate thermal heatgeneration associated with infrared radiation. This enables the UVgenerator 48 to be placed closer to the fabric 32B during treatment toachieve photodegradation without also causing thermal softening and/orcover deformation. FIGS. 13 and 14 illustrate a variation of the UVemitting apparatus of FIG. 12 in which the UV blocking template 82 isattached as a bottom panel of a UV generating unit 48 as opposed tobeing a separate independent piece as shown in FIG. 12. The remainingfeatures and operation, however, are the same as those described abovein connection with FIG. 12. As shown in FIG. 14 the UV generator 48 maybe suspended over the fabric as roll goods or as sheet stock 90 after ithas been woven or knitted and the radiating of the fabric by thegenerator may take place on the front or the back side of the sheet. Theresultant sheet of fabric with weakened tear seam area may then bebackfilled to produce a trim panel. Finally, the substrate layer wouldbe weakened from the backside by laser or knife means in an area thatunderlies the weakened tear seam 36B. A further alternative includesradiating the fabric with UV radiation over the entire area of the door14B rather than just in the tear seam region 16B. In addition tocontrolling the UV generator 48, the cover fabric 32B itself may,through appropriate selection of UV inhibitors and promoters, beformulated to control the susceptibility of the material tophotodegradation in the prescribed wave lengths mentioned above. This isachieved by including appropriate UV inhibitors and/or promoters in thepolymeric material of the air bag cover fabric 32B.

In another construction, a polyester yarn is woven or knitted into afabric. The fabric layer 32B is then cut into a blank and a mask appliedto the surface of the fabric, either to the front side or back side, themask covering the surface of the fabric except for an opening in themask which will outline the cover portion over the air bag door. Asodium hydroxide solution is applied to the unmasked portion of thefabric. The fabric is then preferably heated with steam to activate thesodium hydroxide and finally rinsed with water to remove the sodiumhydroxide. The treated area of the polyester fabric has substantiallyreduced tensile strength compared to the masked area of the fabric suchthat when the fabric is molded behind and formed into a trim panelcontaining an air bag door portion, an air bag can burst through thedoor opening, the door hinged to cause preferential tearing of theweakened fabric in a prescribed pattern adjacent the air bag. The maskmay define an area to be treated including, but not limited to, theshape of an “X”, “I”, “H”, “U” or an enclosed shape such as a circle orrectangle. Optionally, a caustic treatment may be applied to fabric rollgoods as they are being manufactured, in which case it may be preferredto mask and treat a strip of fabric across the roll rather than adiscrete area. When a blank is cut to form a trim panel, care must betaken to align and register the weakened strip with the air bag doorformed in the substrate to ensure optimal air bag deployment. A processsimilar to that shown in FIGS. 12-14 may be used to mask of the fabricfrom the caustic spray. The UV generator 84 would be replaced with a setof nozzles confined in a chamber to apply the caustic solution throughthe opening 86 in the template 82 and onto the surface of the fabric.

An additional construction for weakening a fabric cover stock for use asan air bag cover includes the manufacture of fabric wherein fibers oryarn of weaker strength are specifically woven into the fabric in apattern and in a discrete area to form a weakened area which maycomprise the air bag cover layer for a trim panel. In this embodiment,when the fabric is manufactured, preferably woven or knitted, weakeryarns of lesser tensile strength are introduced into the weaving orknitting process at such time that they will form a preferred pattern inan area of the fabric which later will become the air bag door cover.The weaker yarns used would preferably be indistinguishable with thenaked eye from the normal yarns such that the weakened area remainsinvisible until an air bag is deployed through it causing the fabric totear preferentially. In a weaving process, the use of weaker yarns in a“plaid” or crossing strand pattern which would preferably form arectangle of weaker fibers in the shape and size of an air bag doorwould be registered in the injection mold to roughly coincide the airbag door opening in the trim panel. A preferred density of the weakeryarns may be one (1) out of twenty (20) of the yarns of normal strength.The weaker yarns may be formed by a difference in yarn size denier, theuse of yarn of a relatively lower average polymeric molecular weight,the use of yarn of a relatively lower degree of orientated polymer, theuse of yarn exposed to a heat annealing treatment, and the use of yarnweakened by treatment by a chemical agent, such as caustic, or anycombination thereof of all the aforementioned weakening options. Inaddition, with respect to knitted fibers, a similar means of weakeningduring manufacture of the fabric is possible, whereby the tricot knitcan include weakened fibers included in the longitudinal direction(warp) and weft insertion may be used to include weaker fibers in thedirection across the roll.

The construction of the fabric layer in this embodiment of the presentinvention is shown in simplified diagrammatic form in FIGS. 15 and 16.In FIG. 15, a section of a fabric layer is shown at 32B which comprisesyarn woven or knitted in a pattern of interengaging warp and fill (orwales and courses) or warp and weft threads or yarns. The length of thewoven fabric 32B is formed of warp threads 92 extending longitudinallyin the direction of the length of the woven fabric 32B as well as weftthreads 92′ extending essentially transversely across the width of thewoven fabric 32B. Fibers or yarn of lesser tensile strength 94 areinterwoven or knitted in a relatively narrow band (designated as B) inthe fabric to provide a strip across and/or along the fabric which willtear more easily than the rest of the fabric (designated as A). Theweaker yarn 94 has an appearance indistinguishable from the rest of theyarn 92 and thus may be woven below the top surface of the fabric oralternately near the top surface of the fabric. FIG. 16 shows asectional view of the woven or knitted fabric. While the weaker yarn isshown as smaller in diameter in the FIGS., this would not need to be thecase in actuality as the weaker yarn may be weakened by chemical,radiation or composition means and not need to be of less diameter.

FIG. 15A diagrammatically illustrates a similar construction for aknitted fabric with a weaker yarn indicated at 94′ and the standard yarnat 92”. FIGS. 17-20 illustrate two of many possible configurations ofweakened fabric patterns that may be used to provide a weakened fabriclayer for use over an air bag system. In FIG. 17, the weaker yarns 94are provided in a rectangular pattern of weakening as the yarn is wovenor knitted in both a longitudinal and lateral direction. When the fabricis cut into blanks or sheets, indicated at C for forming the air bagcover, the area indicated at D would be registered to the mold cavitysuch that when backfilled with polymer it would overlie the air bag doorportion molded into the trim panel. Alternatively, as shown in FIG. 18,the weakened yarn 94 may be woven into the fabric 32B in a band thatextends across or along the web of fabric and provides an area ofweakening that extends across the entire trim panel. The band ofweakness 94 may only cover the rear-most edge of the air bag door,nearest the occupants of the vehicle, or may extend the full depth,front to rear, of the door outermost surface. Conversely, the yarns 94(either knitted or woven) in FIG. 17 may be significantly stronger thanthe surrounding yarn 92 such that upon air bag deployment the air bagdoor area severs at the surrounding stronger yarn 94 to preferentiallytear open.

It is further possible to weave or knit a fabric having a discretepattern woven into the area designated to overlie the air bag door toform a weakened area in the shape of the door (“U”, “I”, “H”, “X”) suchas a plaid or embroidered cloth is manufactured with the weaker yarnscomprising a higher percentage of the fabric in the area which willbecome the air bag door cover. Blanks may then be cut from the fabricroll goods to form sheets which may be delivered to an injection mold ina preformed or unformed state and registered to the mold surface suchthat the pre-weakened area is located in the area of the air bag doorportion of the trim panel. Once backfilling of the panel is completed,the substrate may be further weakened from the backside by laser orknife cutting to demarcate the air bag door from the trim panel portion.

Yet another means of weakening a fabric an/or leather, polymeric filmsand other rolled goods material that can be used as a cover for an airbag assembly, as disclosed herein, includes the use of a laser appliedto roll goods as they are being manufactured to weaken discrete areas ofthe fabric which will overlay an air bag door. Current uses of lasers inthe fabric industry include cutting of fabric, engraving designs oncarpets, fixing dyes or heat treating unbleached or bleached goods so asto impart improved adhesion properties, and scribing graphics on to theface of a material for aesthetic reasons. The concept of applying alaser to the back of a fabric material for the controlled alteration ofphysical properties, specifically to pre-weaken the fabric, leather,polymeric films and other rolled goods, for use as a trim cover for anair bag door, is provided herein. Types of properties affected by thelaser include, but are not limited to, tensile strength, tear strength,elongation, recovery, gas or liquid permeability, sound absorbing andpliability. It has been found that with proper selection of laseroperating parameters, such as speed, power level, frequency, wavelength,etc., that the strength of a woven or knitted fabric, leather, polymericfilm, etc., may be reduced locally. It is also important to note thatsuch strength reduction can be achieved without altering the surfaceaesthetics. Or, stated another way, the strength reduction is not theresult of cutting or engraving, and substantially avoids such physicalalteration of the fabric, leather or polymeric film material.

Expanding upon the above, this technique provides a means throughprogramming of a robot which directs the laser to provide a weakenedpattern for a fabric, leather or polymer film layer to be used as acover over an air bag. According to the present invention, e.g., a laseris directed onto the backside of a fabric outer layer which is to beused as the cover for an air bag system. The laser energy density perunit time (see, e.g., U.S. Pat. No. 6,252,196B1) can be altered to varythe impact on material properties. The laser is driven by a robot toproject the laser beam onto the back surface of the fabric and focus thelaser energy in a pattern in the fabric which closely resembles theshape of the outline of the air bag door which the fabric will overlay.Upon activation of the laser, the area of the fabric encountering thelaser beam is significantly weakened without any appreciable change inaesthetics. Stated another way, no physical cut, e.g., is applied to thefabric, leather, or polymeric film, but the fabric, leather and/orpolymeric film is nonetheless strategically weakened by the laserexposure.

Table I and II describe the effect of laser treatment on the back of apolyester knitted fabric using different laser parameters. FIG. 19 is aschematic view of a polyester knit tricot fabric layer of about 315grams/square meter, which has been treated with a CO₂ laser using threedifferent weakening patterns, a “dot” pattern (a), a “horizontal line”pattern (b) in the course direction of the fabric and a “vertical line”pattern (c) in the wales direction of the fabric. The laser wasprojected onto the fabric layer at two different power levels. Samplesfor tensile and elongation testing were cut in the both wales and coursedirections from all three areas weakened by treatment with the laser asshown in FIG. 19, and compared to the tensile and elongation samples ofuntreated fabric. The difference between the “dot” pattern (a) and the“line” patterns, (b) and (c), is the duration of time and the pulse rateof the laser as it is moved relative to the fabric. TABLE I TensileStrength of Fabric Dot Pattern Dot Pattern Wales Direction CourseDirection Original 350N 850N Power Level 50 210N 480N Power Level 60135N 340N Horizontal Line Horizontal Line Wales Direction CourseDirection Original 290N 730N Power Level 45 220N 420N Power Level 55220N 265N Vertical Lines Vertical Lines Wales Direction Course DirectionOriginal 300N 730N Power Level 45 140N 520N Power Level 55 100N 435N

TABLE II Elongation of Fabric Dot Pattern Dot Pattern Wales DirectionCourse Direction Original 75% 135%  Power Level 50 86% 70% Power Level60 51% 65% Horizontal Line Horizontal Line Wales Direction CourseDirection Original 70% 105%  Power Level 45 65% 70% Power Level 55 64%56% Vertical Lines Vertical Lines Wales Direction Course DirectionOriginal 69% 105%  Power Level 45 44% 82% Power Level 55 38% 77%

FIG. 20 is a diagrammatic view of a laser 100 driven by a robot 102being projected onto the backside of a fabric layer 32C to provideweakening in a discrete pattern 36C to be formed over an air bag doorportion of a trim panel to weaken the fabric in a pattern resembling theouter periphery of the door and insure predictable tearing of the fabriclayer and deployment of the air bag. Laser treatment of a fabric layerto weaken the fabric in a discrete pattern to essentially match theoutline of an air bag door may also be carried out on the front surfaceof the fabric layer, or alternatively on the front surface of a formedtrim panel. The result is a preferentially weakened cover layer having apattern or design on the outer surface which indicates the presence ofthe tear seam. The tear seam may be integrated into a decorative orartistic design.

Referring to FIG. 21, there is illustrated another exemplary embodimentof a fabric covered instrument panel assembly with an integral air bagdoor, as previously described. This is an enlarged cross-sectional viewsimilar to FIG. 2. The instrument panel assembly may generally include afabric outer layer 32D that is disposed over a backing layer 34D, whichis, in turn, disposed over a substrate 20D. An air bag door 14 isdefined in the substrate 20D by a line of mechanical weaknesscircumscribing the perimeter of the air bag door 14. According to theexemplary embodiment, the line of mechanical weakness defining the airbag door 14 includes tear seams, generally indicated at 26D and 26D′.

The aspect of the invention illustrated in FIG. 21 differs from thepreviously described embodiments in that the tear seam 26D correspondingto the hinge region of the air bag door 14 does not includepre-weakening of the fabric layer 32D. Preferably, the tear seam 26D′circumscribing the remainder of the air bag door 14 includespre-weakening of the fabric layer 32D. According to the illustratedembodiment, pre-weakening of the fabric layer 32D along the tear seam26D′ may include local thinning of the fabric layer 32D. Consistent withthis configuration, during air bag deployment, the tear seam 26D, 26D′fails allowing the air bag door 14 to open in a predictable manner.Along tear seam 26D′, failure of the tear seam includes rupture of thefabric layer 32D along the tear seam 26D′, therein allowing the air bagdoor 14 to open. However, because the fabric layer 32D is notpre-weakened along the region of the tear seam 26D corresponding to thehinge of the air bag door 14 desirably remains intact.

Consistent with this aspect of the invention, the fabric layer 32D mayserve as an air bag tether system for a fabric covered instrument panelassembly because the fabric layer 32D remains intact in the region ofthe air bag door hinge. Therefore, when the air bag deploys the fabriclayer 32D acts as a large tether for the door and keeps the door inplace. Accordingly, the need for a separate tether system, such as thatindicated by 41 in FIG. 2, may be eliminated.

In order to ensure that the air bag door will be retained by the fabriclayer 32D, it may be desirable selectively reinforce the fabric layer32D in the region of the tear seam 26D in the region of the air bag doorhinge. Such selective reinforcement may be provided by programming thefabric layer 32D with high strength fibers in the region of the tearseam 26D, i.e., provide high strength fibers in the weave or knit of thefabric layer 32D. By high strength fibers it is meant any fiber that hasa higher tensile strength than the nominal fabric layer fiber or yarn.This is generally the converse of the weakening method disclosed withreference to FIGS. 15 and 16. That is, rather than introducing fibers oryarns that are weaker than the nominal fibers or yarns of the fabric,the fabric 32D may be reinforced by locally introducing fibers or yarnsthat are stronger than the nominal fibers or yarns of the fabric.

As alluded to above, the fabric cover stock may be selectivelystrengthened by incorporating fibers or yarn of greater strength intothe fabric in a pattern and in a discrete area to form the strengthenedarea in the region of the air bag door hinge. In this embodiment, whenthe fabric is manufactured, preferably woven or knitted, stronger yarnsof greater tensile strength are introduced into the weaving or knittingprocess at such time that they will form a preferred pattern in an areaof the fabric which later will become the hinge region of the air bagdoor. The stronger yarns used would preferably be indistinguishable withthe naked eye from the normal yarns such that the strengthened arearemains invisible until an air bag is deployed, wherein the strongeryarns do not rupture. In a weaving process, the use of stronger yarns ina “plaid” or crossing strand pattern which would preferably form arectangle of stronger fibers that extend across the hinge region of theair bag door would be registered in the injection mold to roughlycoincide the air bag door hinge region in the trim panel. A preferreddensity of the stronger yarns is selected such that the yarn functionsas a tether. The stronger yarns may be formed by a difference in yarnsize denier, the use of a yarn of a relatively higher average polymericmolecular weight, the use of yarn of a relatively higher degree oforientated polymer, the use of yarn of high tensile strength polymericmaterial, such as Kevlar. In addition, with respect to knitted fibers, asimilar means of strengthening during manufacture of the fabric ispossible, whereby the tricot knit can include strengthened fibersincluded in the longitudinal direction (warp) and weft insertion may beused to include stronger fibers in the direction across selected areasof the roll.

Referring to FIGS. 22 through 24, simplified diagrammatic illustrationsof this mode of providing selective reinforcement of the fabric layerare shown. In FIGS. 22 through 24 a section of fabric layer 32D is shownincluding yarn woven or knitted in a pattern of warp and fill (or walesand courses) or warp and weft threads or yarns. The length of the wovenfabric 32D is formed of warp threads 200 extending longitudinally in thedirection of the length of the woven fabric 32D, as well as weft threads200′ extending essentially transversely across the width of the wovenfabric 32D. Fibers or yarns of greater tensile strength 202 areinterwoven or knitted in a band (designated B) that is arranged suchthat it will span the hinge region of the air bag door. Preferably thestronger fibers 202 have an appearance that is indistinguishable fromthe rest of the yarn 200, and thus may be woven below the top surface ofthe fabric or alternatively near the top surface of the fabric. FIG. 23shows a sectional view of the woven or knitted fabric. In addition, thehinge is preferably positioned such that the hinge line 201 isperpendicular to the fibers 202 of greater tensile strength. However,while a hinge line at such 90 degree angle to the fibers 202 ispreferred, it can be appreciated that the hinge line can vary anintersect with the fibers 202 at angles greater than 90 degrees, up to179 degrees, and at all 1 degree increments therebetween, whichtherefore still provides at least a portion of the fibers span the hingeline and exert a strengthening effect.

Referring to FIG. 24, a similar construction for a knitted fabric isshown including a stronger reinforcing yarn 202′ and a weaker yarn 200″making up the majority of the fabric. As shown, the stronger yarn 202′forms a band (or several bands) within the knitted fabric. The size ofthe bands will, of course, depend upon the degree of reinforcementnecessary.

According to this aspect of the invention, further embodiments mayinclude tear seams 26D, 26D′ provided by pre-weakening of the instrumentpanel assembly in general, and the fabric outer layer 32D in particular,according to any of the methodologies or mechanisms describedhereinabove. Such pre-weakening may include weakening of the fabriclayer from the front side of the instrument panel, weakening the fabriclayer from the back side of the instrument panel, or weakening thefabric layer internally. Methods of pre-weakening the fabric layer 32Dalong the tear seam 26D′, and corresponding structures, have beenthoroughly described above.

The specific features of any single embodiment discussed herein andshown in all the appending FIGS. are applicable and interchangeable toany and all of the embodiments shown herein.

The description and drawings illustratively set forth the presentlypreferred invention embodiment. We intend the description and drawingsto describe this embodiment and not to limit the scope of the invention.Obviously, it is possible to modify these embodiments while remainingwithin the scope of the following claims. Therefore, within the scope ofthe claims one may practice the invention otherwise than as thedescription and drawings specifically show and describe.

1. An air bag cover for an air bag safety system for a vehiclecomprising: a fabric outer layer having a front side and a backside, asubstrate containing an opening, said opening closed by an airbag door,said door having a periphery at least a portion of which comprises adoor/substrate tear seam, the substrate formed by low pressure moldingat a clamp pressure of less than or equal to about 1000 psi., whereinthe fabric outer layer overlies the opening in the substrate, andwherein the fabric outer layer is weakened at a location a portion ofwhich is located outboard of said door/substrate tear seam.
 2. The airbag cover of claim 1, wherein said door is formed integrally with saidsubstrate, said door having an outer edge.
 3. The air bag cover of claim1, wherein the fabric outer layer includes a backing layer positionedbetween said fabric outer layer and said substrate.
 4. The air bag coverof claim 1, wherein said fabric outer layer is weakened by partiallycutting into the backside of said fabric outer layer.
 5. The air bagcover of claim 3 wherein said weakening of said fabric outer layerincluding said backing layer is provided by cutting with a laser orknife.
 6. The air bag cover of claim 3, wherein at least one of saidfabric outer layer, said backing layer or said substrate are weakened bythe application of a knife or a laser and at least partially cuttingthrough any one of said fabric outer layer, said backing layer or saidsubstrate.
 7. The air bag cover of claim 4 wherein the fabric outerlayer is weakened in a pattern that lies just outside of the opening inthe substrate that is closed by the door.
 8. The air bag cover of claim1 wherein said low pressure molding comprises one of sequentialinjection molding, reaction injection molding, injection-compressionmolding, gas assist injection molding, structural foam molding, gascounter-pressure injection molding, and extrusion molding.
 9. A methodfor forming a trim panel for concealing an air bag system, said trimpanel having a molded substrate, said substrate having first and secondopposing surfaces and a fabric applied to said first surface, the methodcomprising the steps of: (a) providing a mold assembly having coactingfirst and second mold members, the first mold member having a cavityportion disposed thereon and the second mold member having a detailportion disposed thereon, said first and second mold members beinginterchangeable with each other such that the cavity and core portionscooperatively define an interior cavity of said mold assembly; saidcavity portion having a series of blade members extending therefrom tosubstantially engage with said core portion when said mold assembly isclosed, said blade members disposed in a pattern that at least partiallyoutlines the periphery of said door; (b) providing a sheet of fabric forapplication to said trim panel; (c) placing the fabric sheet betweensaid coacting first and second mold members in alignment with saidcavity portion; (d) engaging said first and second mold members togetherto form said mold assembly interior cavity; (e) injecting a plasticmaterial into said interior mold cavity to integrally form saidinjection molded substrate and said door and urging the sheet of fabricinto contact with the surface of the cavity portion including the bladeportions extending from the cavity portion; and (f) removing said trimpanel from said mold assembly; and weakening said fabric in the slotsformed by said thin blade members.
 10. The method of claim 9 whereinsaid fabric is weakened by a cut via projecting a knife or laser throughsaid slots formed in said trim panel wherein said cut is eitherpartially through or completely through said fabric.
 11. The method ofclaim 9 further wherein said step of providing a sheet of fabricincludes providing a sheet of fabric containing a backing layer.
 12. Themethod of claim 11 wherein said weakening of said fabric includesweakening of said backing layer.
 13. The method of claim 12 wherein saidweakening of said backing layer comprises cutting either partially orcompletely through said backing layer.
 14. A method for forming a trimpanel for concealing an air bag system, said trim panel having a lowpressure injection molded substrate, said substrate having first andsecond opposing surfaces and a fabric applied to said first surface, themethod comprising the steps of: (a) providing a mold assembly havingcontacting first and second mold members, the first mold member having acavity portion disposed thereon and the second mold member having adetail portion disposed thereon, said first and second mold membersbeing interchangeable with each other such that the cavity and coreportions cooperatively define an interior cavity of said mold assembly;(b) providing a sheet of fabric for application to said trim panel; (c)placing the fabric sheet between said contacting first and second moldmembers in alignment with said cavity portion; (d) engaging said firstand second mold members together to form said mold assembly interiorcavity; (e) injecting a plastic material into said interior mold cavityto integrally form said low pressure injection molded substrate and saiddoor and urging the sheet of fabric into contact with the surface of thecavity portion; and (f) removing said trim panel from said moldassembly; and weakening any one of said fabric sheet or said substrate.15. The air bag cover of claim 14, wherein at least one of said fabricouter layer or said substrate are weakened in by the application of aknife or a laser and at least partially cutting through any one of saidfabric outer layer or said substrate.
 16. The trim panel of claim 14further including wherein the fabric sheet includes a backing layer. 17.The trim panel of claim 16, wherein at least one of said fabric sheet,said backing layer or said substrate are weakened in by the applicationof a knife or a laser and at least partially cutting through any one ofsaid fabric outer layer, said backing layer or said substrate.
 18. Thetrim panel of claim 14 wherein said low pressure molded substrate isformed by one of sequential injection molding, reaction injectionmolding, injection-compression molding, gas assist injection molding,structural foam molding, gas counter-pressure injection molding, andextrusion molding.